Hi there, I've been searching for an answer to my question high and low for hours now and I can't figure out anything. My biology class did the paper chromatography experiment to separate chloroplast pigments. The peaks on the absorption for chlorophyll a and b differ between plants and I can't figure out why, beside major errors in the experiment. From what I can tell, chlorophyll a and b always have the same exact molecular makeup, but can anything bind to either pigment molecule to affect its absorption spectra? For instance, can a protein or a mineral bind to chlorophyll a to make it absorb light in a different way than it absorbs light in a different plant?

This is an educated guess... can I stress that?You know chlorophyll's poryphrin ring, right? It has a magnesium in the middle. First, is that chlorophyll a? And if so, can that be a different metal ion (and make it chlorophyll b)?

I'm talking about the results for both chlorophyll a and b. One of our plants has both chlorophyll a and b peaking at totally different wavelengths than the other plants, so I just thought it would be cool to talk about the variance in chlorophyll molecules because of things becoming ionized, or bonding, or who knows what. I thought the results would allow for a cool topic instead of "plants like blue light more than red", you know? But as far as what you're saying, if the Mg does become ionized, will that affect the way that it excites under light? Will that change the wavelengths that it peaks at?

One thing to consider, the plant that has really odd chlorophyll a and b peaks is a plant heavy in anthocyanin. I can't for the life of me figure out how anthocyanin would affect separate chloroplast pigments though... it's not like the anthocyanin bonds to chlorophyll from what I can tell, so why would this plant heavy in anthocyanin have shifts in the absorption maxima in chlorophyll a and b? Again, I'm just wondering if the test turned out incorrectly...

First of all, I was wrong. There is a methyl group on chlorophyll a and a carbonyl group on chlorophyll b. The accessory pigments will affect the absorption of different colors of light. Accessory pigments transfer their energy to chlorophyll a. The plant you had must have had differet accessory pigments. I'd guess that anthocyanin moved it away from its normal peak.

I'm just curious though, if the pigments were separated on a chromatography paper, wouldn't that force the anthocyanin into it's own section of the strip, or would it actually physically bond to the chlorophyll causing the chlorophyll pigments to have altered absorption maximas?

noiseordinance, first of all chl a and chl b are not identical in chemical structure, their difference is responsible for their inherently different absorbtion spectra. Now, surrounding molecules can definitely affect the absorbtion spectrum. To realize this, i suggest you look into molecular orbitals, HOMO-LUMO, quantum mechanics and all that jazz. but the long story made short is that because chl is in a photosystem complexed with proteins and other molecules rather than in solution, it has very different behaviours. think of it: chl a in photosystem II absorbs at 680 nm, while chl a in photosystem I absorbs at 700 nm (here I mean the molecules in the center of each photosystem, the ones on the periphery would absorb at slightly shorter wavelengths). Now, anthocian pigments should not influence chl absorption even in vivo, let alone in solution. can you tell me numerically what your data said?

"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

I've taken a fair amount of chemistry and am good on the electron orbitals and all the jazz. I also know that anthocynanins have their own unique absorption spectra that compliments all the other photosynthetic pigments. I just couldn't figure out why all the data for our anthocyanin plant had vastly different absorption in chlorophyll a and b than the chlorophylls presented in our non-anthocyanin specimins. I don't have my data here, but let's just say that the chlorophyll in our anthocyanin plant was shifted inward by about 30-50nm for both sides. That is, if the chlorophyll a in a typical specimin peaked at 450nm and 600nm (I know that's inaccurate, but just trying to illustrate), our anthocyanin plant peaked at 480nm and 570nm.

I'm just trying to figure out if the chlorophyll's polarity or pH could have changed because of the initial presense of anthocyanin, if something could have bonded to the chlorophyll, or if this is likely a mistake in the experiment process.

Anywho, I'd love to do my report on the significance of the peaks being strange in our anthocyanin plant. I'm guessing my idea is a flop though since I'm almost out of time and I can't really find any data about how anthocyanin affects chlorophyll, with the exception of stealing part of it's spectra.

well, if I were to take a shot in the dark I would say it is your chemical environment in the solution that is affecting the properties of chl (pH, redox environment, god only knows, something). I don't think what you are observing is a physiological reaction..

"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter